1. Field of the Invention
This invention relates to a dial gauge, more specifically, a dial gauge intended for decrease of the number of parts and reduction of production costs.
2. Description of the Related Art
A conventional dial gauge includes a case that is composed of: a cylinderical case body supporting a movable spindle in the axial direction passing through the outer circumferential wall of the case body; a front case member provided on the front of the case body and having a digital indicator for indicating a moving displacement amount of the spindle; and a rear case member provided on the rear of the case body.
The three members composing the case are individually formed in advance. In assembling processes, the front case member and the rear case member are assembled onto the case body, resulting in the case.
In the conventional fabrication, the case is composed of three individual members of the case body, the front case member and the rear case member, thereby allowing the large number of parts and the complicated process of assembling. Waterproof and dust-proof structures are required to be formed between the case body and the front case member and between the case body and the rear case member. Therefore the elaborate structure leads to increase of production costs.
As a model of the dial gauges, a dial gauge with an electrostatic capacitance type encoder is known. More specifically, a first scale is formed in a case to support a movable spindle in the axial direction as a sensor for measuring a moving displacement amount of the spindle, and a second scale is formed in front of the spindle opposite of the first scale. Relative stroke of the first and second scales is measured by detecting a change in electrostatic capacitance between electrodes arranged in the first and second scales.
In the electrostatic capacitance type encoder, a uniform gap is formed between the first scale and the second scale. But the gap tends to be narrower by reason of, such as the requirement of great precision and saving of electric power for inputting and outputting signals.
In conventional processes for setting the gap, great precision and complication are required for components for holding the first scale and the second scale with the uniform gap, which is a factor in increase of production costs in commercialization.
In the known structure for setting the uniform gap between the first scale and the second scale, plural projections which each have the height corresponding with the gap are formed on one of mutually opposing surfaces of the scales. The scale, not having the projections, is forced toward the scale having the projections by a plate spring portion of a cantilever support structure. The projections formed on the scale are abutted onto the other scale so as to form the uniform gap between the first and second scales.
However, according to the above fabrication, means for forcing one scale toward the other scale are the plate spring portion of the cantilever support structure, so that the scale is forced toward the other scale in the inclined state. It leads into the difference of the touching pressures to the other scale at each projection. Therefore, when the scales are relatively moved, the gap is easily changed between the scales and the degrees of abrasion vary among the projections, with the result that the gap between the scales cannot be maintained at a uniform space for a long period of time.
It is an object of the present invention to provide a dial gauge with a simplified structure, a decrease in number of parts and reduced production costs to resolve the conventional disadvantages.
It is another object of the present invention to provide a dial gauge which a gap between scales is retained at a uniform space for a long period of time, in addition to the aforementioned object.